HT4100 4.1, 4.5, 4.9 Discussion, Cooling Problems in Cadillac Engine Technical Discussion; I bought an 86 Fleetwood 4.1 (HT4100? what does that mean?) from a cash-and-carry lot (auction-bound). I saw the water ...

Cooling Problems

I bought an 86 Fleetwood 4.1 (HT4100? what does that mean?) from a cash-and-carry lot (auction-bound). I saw the water bottles in the back seat and had second thoughts. The sensors and radiator were new. So was the engine. I took it for a spin and no smoke! I really didn't want to buy it since it probably had a cooling problem, all my other cars are 78's with 200K+, I hate plastic and electronics, but the salesman wouldn't let me go. So I made him grovel and bartered him down from $1800 to $1000. New tires, why not?

I knew nothing about the aluminum "worst engine ever made". It ran OK during the winter in Houston. But summer was too much, hell, spring was too much. I swapped out a good water pump, then parked it for two years.

I have spent the last week checking fan motors, sensors, relays - planning on hot-wiring the fans - I don't know what I am doing and too poor to take it to the dealer. Sometimes one fan works, sometimes two, but never soon enough or long enough. The engine overheats in three minutes if you are not sailing upwind.

Thanks to your forum I now feel confident that all I need is the 160 degree thermostat. The 280 degree one is a little Nordic for the summers down here where the freeway can cook at 200 degrees, 5 mph stop-and-go for 50 miles. I'm sure it was a planned-obsolescence feature.

I'll let you know what happens.

PS. The alternator reads 12.12 volts. 11 with the headlights on. Is that a little shy? New battery, might not be fully charged.

Also the sensor leads show 5 volts only when the ignition is on. Don't the fans need to run after the ignition is keyed off? Have I found the right sensors?

Re: Cooling Problems

280?! No wonder the thing cooks itself. Anyway, 12.12 is very low, take a long hard look at your alternator, it may be wise to get it tested soon as it may be starting to go. Which sensor are you talking about?

Re: Cooling Problems

Originally Posted by DaveSmed

280?! No wonder the thing cooks itself. Anyway, 12.12 is very low, take a long hard look at your alternator, it may be wise to get it tested soon as it may be starting to go. Which sensor are you talking about?

The sensor(s) for the two cooling fans (lateral engine). If I put in the cooler thermostat, will the fans kick in sooner?

I have gotten several different views of how these fans work. The Cad parts man says the smaller fan will turn on only if the A/C is running (A/C is kaput). Will I still have to hot-wire the fans? What do I hook-up to? Accessories? The fan motors are hefty - will there be enough juice? - 12 gauge wire?

Re: Cooling Problems

Proper Thermostat Is 195 Degrees. Putting In A Lower Temp One Will Not Allow The Engine To Go Into Closed Loop At The Proper Time, Causing Poor Fuel Mileage. The Fans Turn On At Approx. 220 Degrees. Using The Wrong Thermostat Will Delay Or Keep The Fans From Ever Coming On. I Don't Approve Of Patch Jobs Like By Passing Sensors. Will Cause Other Problems. Diagnose It Right And Fix It Right. One Fan Reacts To Engine Temp. The Other To Head Pressure In The A/c System. This Engine Easily Gets Air Pockets In It Which Will Give A False Fluid Level In The Radiator. Start With A Cold Engine After Proper Thermostat Installed To Fill The Radiator. Set The Climate Control To Auto And 90 Degrees. Fill The Radiator At Normal Idle, When The Upper Hose Just Starts To Get Warm, Have A Buddy Raise The Idle Manually To Approx 1500 Rpm, Continue To Fill The Radiator While The Engine Speed Is High, That Will Help Purge The Air. Once The Radiator Is Full Reinstall A New Proper Radiator Cap While At Hi Engine Speed. Then Fill The Recovery Tank To Correct Hot Level. If The Fans, Fan Control Modules And Related Sensors Are Good, The Engine Temp Should Stabilize At About 195 To 200 Degrees. Correct Engine Temperature Is Mandatory For The Other Sensors To Work Within Thier Parameters. Knowing How To Monitor The System Thru The Dash Diagnostics Is Very Important. I Would Recommend A Factory Service Manual. Money Well Spent. Hope This Helps A Bit, Bill.

Re: Cooling Problems

It Is Also Very, Very Important That You Install The Cadillac Cooling System Pellets When Replacing The Antifreeze. The Pellets Are Available Thru Any G.m. Dealership Or Barsleak Gold Brand Radiator Sealer Available At Most Auto Parts Houses. Same Formula, Different Packaging. If Using The Pellets, Smash The Pellets In The Package Before Pouring In The Radiator. Please Report Back On Outcome For The Rest Of Us!

Re: Cooling Problems

I have heard this advice before - put everything back to specs and it will work. I have also read several other people on this forum with the same engine saying they have spent $thousands replacing everything in the cooling system and still overheats.

If the radiator was giving a false fluid level, this would allow the engine to heat up, and the fans should turn on at some point. But they don't.

I have had cooling problems in other cars due to the heat in Texas, long idling on the freeway. The clutch fan not turning at idle is counter-intuitive. The assumption is that, when idling, your engine will be cold. A flex fan solves the problem permanently - never overheats again. Won't solve this problem, though, the engine is sideways.

I know that if air is not pulled through the radiator, the engine will overheat - no matter what car or engine. On this one, the electric fans do not turn on soon enough, if at all, and once on, they don't stay on long enough. The engine continues to heat up until the hot light comes on. These aluminum engines are notorious for overheating and self-destruction, so I park the car until it cools rather than continuing to drive it with the hot lamp on - not sure if at some point the fans will start and the hot light will go off - is that standard operation?

The engine and radiator have been replaced once. All the visible sensors have been replaced. The fans have been bench checked at least twice, once by previous owner, and by me. There is no coolant leaking problem. I will check the codes on the climate control and come back (I don't have a manual).

I don't mean to be argumentative - I am not a mechanic, but three mechanics have thrown up their hands on this problem already and I parked the car for two years. I don't have $thousands to restore the car to factory floor. I do have some wire to hook the fans to the accessories switch. I just don't know if that will burn something else up.

Re: Cooling Problems

I definitely understand where you are coming from. I am not too familiar with your car, but what exactly triggers the fan relays? The sensor or the BCM? If it's the BCM, Leave the sensors alone. I would recommend wiring both fans together, leaving them connected to the relay from the BCM if it's the BCM that controls them (for A/C control) in addition to the Fan-Thom II on this page (http://www.painlessperformance.com/relays.htm) or something similar to it. The #30102 looks like it would work very nicely with a 195 t-stat.

Re: Cooling Problems

BCM is body control module, it's the thing that controls the climate control among other things. The ECM, engine control module controls engine related stuff, so thats probably connected to the fans as well. Odd that the climate control readout doesn't work. Does the climate control itself work?

Re: Cooling Problems

Originally Posted by DaveSmed

BCM is body control module, it's the thing that controls the climate control among other things. The ECM, engine control module controls engine related stuff, so thats probably connected to the fans as well. Odd that the climate control readout doesn't work. Does the climate control itself work?

nO. The climate control is dead, so is the fuel center.

Where are the fuses? Do I rip out the panelling under the dash? Are they in the trunk? I can't identify a fuse box on the firewall.

Obviously, it didn't come with a manual. I'm searching the internet.

If the HT4100 is fuel injected, mine isn't. I poured gas down the throat of something to get it started. Looks like a carburetor with a coffee can chimney. Runs real smooth.

Re: Cooling Problems

ALL HT4100s were EFI. They used 2 big injectors in a TBI setup which kinda resembles a 2 bbl carbureator. The coffee can thing is a shroud to compensate for the added heighth of the injectors above the throttle body. Theres fuse panels all over that car, but someone will chime in with the correct ones to check.

Re: Cooling Problems

on my '93 DeVille with the 4.9 (same basic style though) I have a fuse box under the dash, like above where my left foot is, you push the tabs in and it folds down, there is also one in the engine bay near the fire wall, and IIRC, one near the firewall when you remove the glove box....